> This makes Tailwind seem like a lot of machinery (in the sense of bundle size, running code, and pseudo-language) just to avoid opening a file at dev time.

It’s not about avoiding opening a file. It’s about avoiding the risk and/or cost that comes from editing a stylesheet that applies globally. If you change existing rules, you risk breaking the layout somewhere you didn’t anticipate. Or, to avoid that, you treat the stylesheet as append-only, leaving you eventually with enormous files and selectors of ever increasing specificity.

Tailwind (or Tachyons) makes for ugly markup, but it solves a real problem, and it does it better than anything else.